1. Field of the Invention
This invention relates to a process for the preparation of alkylene glycols from the corresponding alkylene oxide in the present of water and an amphoteric catalyst, such as (ethylenedinitrilo)tetraacetic acid (EDTA). A specific example of the process is in the preparation of ethylene glycol from ethylene oxide.
2. Description of the Prior Art
The production of alkylene glycols from alkylene oxides is known and is practiced commercially. Of particular interest is the production of ethylene glycol from ethylene oxide. The thermal hydration of ethylene oxide produces monoethylene glycol (MEG). MEG is mainly used as a base material in the production of polyester fibers, resins, films and bottles and is also a major active component in antifreeze.
Hydration of ethylene oxide can be through catalytic and non-catalytic means. Non-catalytic hydration of ethylene oxide to MEG requires a large excess of water to inhibit the formation of diethylene glycol (DEG) and other higher glycols. Even with a large excess of water the molar selectivity to MEG is only about 90%. In addition, the water must be distilled from the glycol to obtain a high purity product.
While the hydrolysis reaction can proceed uncatalyzed, the presence of acids or bases can enhance the rate of reaction. However, strong acid catalysts and strong base catalysts do have shortcomings. For instance, base catalysts generally do not beneficially affect selectivity to the formation of the monoglycol product and the use of acid catalysts typically is accompanied by corrosion problems. Hence, commercial processes typically utilize relatively neutral hydrolysis conditions (for instance, pH 6-10).
Catalytic hydration of ethylene oxide may use smaller amounts of water and is carried out at lower temperatures than non-catalytic thermal hydration. There are numerous examples of catalysts for hydration of an alkylene oxide to alkylene glycol.
U.S. Pat. No. 6,153,801 discloses preparation of alkylene glycols by reacting an alkylene oxide with water in the presence of a polycarboxylic acid derivative catalyst, preferably immobilized on a solid support. When a strongly basic anion exchange resin is used as the support, amines or phosphines may leach from the resin into the product stream. A guard bed of a strongly acidic ion exchange resin may be used to capture the amines and phosphines. When only the H+ form of the strongly acid resin used as a guard bed, the product stream-may become acidic. Using a mixture of the strongly acidic ion exchange resin in its H+ form and salt form in the guard bed keeps the pH of the product stream close to neutral.
U.S. Pat. No. 5,798,412 discloses a process in which carbon is used to selectively catalyze the hydrolysis of alkylene oxides to monoalkylene glycols. It is disclosed that the hydrolysis reaction may be carried out at any pH but a reactant system typically has a pH of between about 5 and about 10, and most typically between about 6 and about 8.
U.S. Pat. No. 4,967,018 discloses a process for catalytic hydrolysis of an alkylene oxide to an alkylene glycol using catalysts based on anionic clay minerals, such as aluminum and magnesium or nickel hydrotalcite-type or takovite-type materials. In general, the pH of the liquid reaction system is between about 3 and 13, preferably between about 6 and 9.
U.S. Pat. No. 4,937,393 discloses a method of manufacturing ethylene glycol with a catalyst of a carboxylic acid and a carboxylic acid salt or a metal salt of formic acid alone.
U.S. Pat. No. 4,620,044 discloses hydrolysis of olefin oxides to corresponding glycols by a steam stable zeolite in its acid form characterized by a constraint index of about 1 to 12.
U.S. Pat. No. 4,551,566 discloses a process for the liquid phase hydration of alkylene oxides to the corresponding alkylene glycols with a vanadate salt and a pH between about 5 and 12. The particular vanadate species present is thought to be dependent on the pH of the liquid phase. Hence, at a pH of, say, about 12, little, if any, metavanadate anion may exist. Although the processes are carried out by providing a water-soluble vanadate salt to the reaction system, the exact nature of the catalytic species is not fully known.
U.S. Pat. No. 4,393,254 discloses a process for hydrating alkylene oxide in the presence of a partially amine-neutralized sulfonic acid catalyst to produce alkylene glycol.
U.S. Pat. No. 4,277,632 discloses a process for reacting an alkylene oxide with water in the presence of a catalyst having molybdenum and/or tungsten to produce an alkylene glycol. The pH value of the reactant solution need not be specifically limited but may be varied in a wide range such as from 2 to 12. Better results of the reaction are obtained when the pH value is limited to the range of from 5 to 10, desirably from 6 to 8. The hydration of the alkylene oxide produces the best results when it is carried out with the pH value kept in the neutral point of about 7. Any acidic or alkaline substance can be used as an agent for keeping the pH value of the reaction solution in the range of from 5 to 10.
EDTA ((Ethylenedinitrilo)tetraacetic acid, also referred to as ethylenediaminetetraacetic acid) is a known compound. US 2003/0073580 discloses EDTA as a chelate for metals in fertilizer mixtures.
U.S. Pat. No. 6,803,167 discloses salts of EDTA as a surfactant component of a developer in the preparation of lithographic printing plates. A mixture of a salt of EDTA and EDTA is discloses as a buffer system to keep the pH relatively constant.
Amphoteric compounds are known as catalysts. U.S. Pat. No. 4,330,666 discloses a method for making polyetherimides by intercondensation of aromatic bis(ether anhydride) and organic diamine in the presence of an amphoteric catalyst, such as hydroxypyridine.